Maternal pre-pregnancy morphine exposure: transgenerational consequences on anxiety-like behaviors and epigenetic-related genes.

Background: Studies have shown that chronic morphine exposure results in altered patterns of gene expression through epigenetic mechanisms, suggesting potential transgenerational effects on the offspring's epigenome.Objectives: This study investigated transgenerational consequences of maternal pre-pregnancy chronic morphine exposure on offspring anxiety-like behaviors and alterations in epigenetic-related genes miR-96, miR-137, MeCP2 and HDAC2.Methods: Adolescent female Wistar rats had access to morphine (0.4 mg/mL) in drinking water (controls: tap water) for 50 days before mating with morphine-naïve males. Offspring underwent the forced swim test (FST) and open field test (OFT) to assess anxiety-like behaviors. Gene expression was analyzed in hippocampus from offspring and ovarian tissue from dams.Results: Offspring from morphine-treated dams exhibited significant increases in floating time (F1, 20 = 43.5; p < .001) and spent time in the center area of the OFT (F1, 20 = 68.1; p < .001). MeCP2 and HDAC2 gene expressions were significantly increased in the ovarian tissue of morphine-treated dams (MeCP2: t10 = 4.3; p < .01; HDAC2 t10 = 8.6; p < .001). In offspring of morphine-treated dams, MeCP2 (F1, 20 = 37.5; p < .001) and HDAC2 (F1, 20 = 62.6; p < .001) expression in the hippocampus was significantly increased, whereas miR-137 (F1, 20 = 25.5; p < .001) and miR-96 (F1, 20 = 23.8; p < .001) expression was significantly decreased.Conclusions: These findings underscore that maternal preconception morphine exposure induces neurobehavioral deficits across generations, likely mediated by epigenetic memory in the maternal germline. This suggests preconception opioid exposure could affect offspring's mental health and stress phenotypes, underscoring the need to integrate screening, counseling, and harm reduction into reproductive and addiction care.